Valves have been provided with shafts in various forms for enabling control of a valve element interiorly of a valve body by control devices located exteriorly of the valve body or sensing spool position with a sensor located exteriorly of the valve body. To prevent leakage of fluid along the shaft, various types of shaft seal arrangements have been provided.
FIG. 1 illustrates a portion of a known hydraulic valve 20. The hydraulic valve 20 has a spool 21 that is movable axially through a spool bore 22 for controlling fluid flow through the valve. A shaft 24 is fixedly attached to the spool 21 and extends outside of a valve housing 25. A seal 26 is associated with the shaft 24 so as to prevent fluid migration out of the valve along the shaft. This sealing configuration is often referred to as a fixed seal design, wherein the seal 26 is fixed relative to an adapter 27 that is threadedly received in a threaded bore 28 in the valve housing 25. To ensure proper alignment of the shaft 24 and seal 26 during assembly of the valve, the threads of the housing bore 28 must be aligned concentrically with the spool bore 22. The shaft 24 also must be concentric with the spool 21 and the fixed location of the seal 26 in the adapter 27 must be concentric with the threads of the adapter so that, when the adapter is threadedly connected to the valve housing 25, the seal 26 will be concentric with the shaft 24. All of this alignment or concentricity requires very precise tolerance control of the valve parts. This required precision usually results in high manufacturing costs of the valve parts. When such tolerance control is not achieved, the seal 26 may not properly seal against the shaft 24 and fluid may migrate out of the valve along the shaft.
FIG. 2 illustrates another prior art fixed seal design. The design shown in FIG. 2 is similar to the design of FIG. 1. The difference resides in the spool 21 and shaft 24. In the valve of FIG. 1, threads are used to attach the shaft 24 to the spool 21, whereas in the valve of FIG. 2, a “T” slot 30 is used. The “T” slot allows the shaft 24 to shift transversely relative to the spool 21, but the “T” slot is an expensive feature to add. Again, with the design illustrated in FIG. 2, precision manufacturing is required so as to provide concentricity of the valve parts. Also, in FIG. 2, the seal 26 is located in a defined groove in the adapter 27. This groove is difficult to machine and requires a high precision tolerance.
FIG. 3 shows yet another prior art design that is similar to the design of FIG. 2. In this design the “T” slot 30 is machined into the shaft 24 with the receiver machined in the spool 21. A spring-loaded washer 32 holds the shaft seal 26 in a groove in the adapter 27 that must be machined with high precision. The concentricity issue is not alleviated with this design. The seal groove particularly must be concentric with the threads of the adapter 27 and the valve housing 25. FIG. 3 also shows a shaft control mechanism 33.